France vs North America slope grading

Hi all - planning a trip to 3 Vallees and wondering how the slope grading compares. Specifically, I'm trying to understand how difficult a red run is as a cautious intermediate skier. Is it comparable to a blue-black at US resorts or more of a single black? For reference I am generally comfortable on blues and blue-blacks at US resorts like Mammoth and Snowmass, but found the blue runs at Whistler to be much harder and steeper. If anyone could compare a red run at 3 Vallees to the runs at any of the above North American resorts it would be much appreciated :)